This invention deals generally with heat transfer and more particularly with a capillary loop evaporator that has full thermal contact of the wick with the heat input surface.
A capillary loop and a loop heat pipe are devices for transferring heat by the use of evaporation at the source of heat and condensation at the cooling location, and they eliminate some of the limitations of a simple heat pipe by separating the vapor and liquid movement into different conduits. Thus, liquid fed to an evaporator is evaporated and moves through a vapor transport line to the condenser, and condensate moves from the condenser to the evaporator through a liquid transport line. Typically, a liquid reservoir is constructed in close vicinity to the evaporator and a barrier wick separates the liquid in the reservoir from the vapor in the evaporator while moving liquid into the evaporator wick by capillary action.
Prior art capillary loop and loop heat pipe evaporators typically have vapor channels at the contact boundary between the evaporator wick and the heat input surface, which is the wall of the evaporator enclosure. The vapor channels are formed as grooves in the wick or the evaporator enclosure inner wall at the boundary, and the lands between the grooves are the only direct thermal path from the heat input surface to the liquid within the wick. From the wick the liquid is evaporated and fed into the vapor channels. The vapor channels then open into a vapor space that is available to the vapor transport line. Some such devices, such as that disclosed in U.S. Pat. No. 6,058,711 to Maciaszek et al, even have the vapor generating wick completely surrounded by the thermally insulating vapor space.
Basic limitations of the typical capillary loop evaporator are the limited direct contact between the wick and the heated surface, and the tendency of the vapor generated at the heat transfer surface to interfere with heat transfer into and through the wick. Another disadvantage of the conventional loop heat pipe evaporator is its proximity and thermal transfer to the reservoir. This phenomenon is referred to as parasitic heat loss or heat leakage, and it causes some heat to be transferred from the evaporator to the reservoir by means of heat conduction across the wick and two phase heat transfer in the central volume which the wick surrounds. Such heat is therefore not moved to the condenser for disposal. Still other problems arise in the difficulty of manufacturing capillary loop and loop heat pipe evaporators since they usually require cylindrical wicks with longitudinal grooves on the outer surface.
It would be very beneficial to have available a capillary loop evaporator that has improved heat transfer from the heat source to the evaporator wick, reduced parasitic heat leakage to the reservoir, and reduced manufacturing complexity.